The present invention relates generally to the field of data migration, and more specifically to migration of stub files.
Hierarchical storage management (HSM) is a data storage technique, which automatically moves data between higher cost and lower cost storage media. Higher-speed storage devices (e.g., hard disk drive arrays) are more expensive per byte stored than slower-speed storage devices (e.g., optical discs and magnetic tape drives). In an ideal situation, data is stored and is available on high-speed devices at all times. However, this may be prohibitively expensive for many organizations. Instead, HSM systems store the bulk of the enterprise's data on slower-speed storage devices and then copy data to higher-speed disk drives when needed. In effect, HSM turns the fast disk drives into caches for the slower-speed mass storage devices. The HSM system monitors the way data is used and determines which data can safely be moved to slower-speed devices and which data should stay on the higher-speed devices.
A stub file is a computer file which appears to a user on a disk and is immediately available for use. The stub file is actually held either in part or entirely on a different storage medium. Upon accessing a stub file, the accessed file is intercepted by a device driver software, data is retrieved from the actual location of the stub file, the retrieved data is written to the stub file, and user access is allowed. Typically, users are unaware that the data within a stub file is stored on a different medium even if there is a slight delay when accessing such a file. Typically, the purpose of stub files is to move data from an expensive higher-speed storage device (e.g., a computer's hard drive) to a cheaper lower-speed storage device (e.g., a magnetic tape or an electro-optical disk) while not requiring the knowledge of using specialized storage software to retrieve the data. Stub files allow a system manager to enforce the use of cheaper storage when users would prefer to store files on the highest availability and higher cost devices. Stubbing is a feature of some commercial file backups, archiving packages, and operating systems.